Hydrometallurgical methods hold an important place in gold-mining industry; they are applied in processing of practically all ore starting materials. Leaching of gold and silver with a cyanide-containing solution underlies the hydrometallurgical methods for processing gold- and silver-bearing ore starting materials.
To recover the gold and silver from the solution, use is made of various methods, such as precipitation, sorption, extraction and the like.
The most promising are hydrometallurgical methods using sorption processes with application of solid sorbents. The principal advantage of these methods is the possibility of effecting the recovery of dissolved valuable elements directly from cyanic pulps, which makes unnecessary expensive power-intensive operations of filtration and washing of the pulp, which, in turn, results in a considerable reduction of capital outlays and operation expenditures, owing to a reduction of working areas and materials and power savings and also in an increased recovery of gold and a silver from ore starting materials, improved quality of finished products, a decrease in the amount of unfinished products and so on.
Known in the art is a method of gold and silver recovery from ores, according to which the starting material is processed at a low density of the cyanic pulp, that is, the content of the solid phase in the pulp is not more than 10% (European Patent No. 9010721, issued in September of 1990).
The pulp after being leached with the solution containing cyanides is held for some definite time, then filtered to separate the liquid phase, containing the dissolved noble metals, from which they are separated by sorption on activated carbon or ion-exchange resin.
The main disadvantage of this method is the use of diluted pulps, which requires large-size equipment and increases the time of the process and the losses of valuable elements with a large volume of the liquid phase and also necessary separation of the solid and liquid phases of the pulp.
It is known to recover gold and silver from ore materials rials by sorption from cyanic pulps on activated, carbon (CIP method). With this method, the pulp is treated with cyanide solutions and a sorbent in the form of activated carbon is then added (L. E. Telegina, L. A. Davydova. Modern State of Sorption Processes for Recovering Gold from Ores Abroad TsNIIekonomiki i informatsii. Tsvetnaya metallurgia. Obogaschenie rud tsvetnykh metalloy. No. 2, 1983, p. 5).
According to this method, an aqueous pulp is prepared from a starting ore material and water, this pulp is alkalized by introducing soluble alkylis to create an alkalinity of about 9.5 to about 11.5 and the alkalized pulp is fed to a reaction zone whereto a cyanide soluble in the liquid phase of the pulp and then granulated activated carbon are fed. Gold, silver and impurities pass to the liquid phase of the pulp due to the reaction with the cyanide and are then absorbed by the activated carbon surfacer and the pulp becomes depleted of gold and silver. After separation of the carbon with the elements absorbed thereby from the pulp depleted of these elements, the carbon is fed to a desorption zone and the pulp is taken off the process. The carbon containing the absorbed elements is treated with a solution of hydrochloric acid to remove part of the impurities and then with an alkaline-cyanic solution for gold and silver desorption with the result of obtaining an Au- and Ag-containing solution taken off the process and carbon depleted of these elements which is fed to a reactivation zone where the carbon is treated with a water vapour at a temperature of about 1000.degree. C. to remove the remaining impurities and to restore its porosity. After this step, the carbon is removed from the reactivation zone and is fed to said reaction zone.
This method features a low content of gold and silver on the sorbent (activated carbon), lower gold and silver concentrations in the solution obtained in the desorption zone, high sorbent losses due to attrition and the need to carry out high-temperature reactivation of sorbent before reuse.
It is also known to recover gold and silver from ore starting materials (ores, concentrates and slimes) by a method using synthetic resin as the sorbent.
This method comprises preparing an aqueous pulp in which an alkalinity is created of about 9.5 to about 11.5 by introducing thereto soluble alkalis to obtain an alkalized pulp which is delivered to a reaction zone which is fed with a cyanide soluble in the liquid phase of the pulp and with a porous grained synthetic sorbent containing anion-exchange groups. Due to the reaction with the cyanide gold, silver and impurities pass to the liquid phase of the pulp as negatively charged ions which are absorbed by the sorbent, resulting in a gold-and silver-saturated sorbent with impurities and a pulp depleted of gold and silver. After separation from the pulp depleted of gold and silver, which is taken off the process, the gold- and silver-saturated sorbent with impurities is delivered to a desorption zone. In the desorption zone, the sorbent saturated with gold and silver and with impurities is treated with a sulfuric acid solution of thiourea containing 80 to 90 g/l thioureau and 20 to 26 g/l sulfuric acid. The volume of this solution of thiourea comprises 10 volumes per the volume of the sorbent. As a result, there are obtained a sulfuric acid solution of thiourea with gold, silver and impurities, which is taken off the process, and a sorbent with a residual content of gold, silver and impurities. In the desorption zone, this sorbent is treated with a solution of sodium hydroxide with a concentration of 25 to 30 g/l as a result of which a solution of sodium hydroxide with impurities is obtained, which is taken off the process, and a purified sorbent which is delivered to a reaction zone.
This method requires a sufficiently high consumption of cyanide, which makes a considerable amount of impurities to pass to the liquid phase of the pulp. As a consiquence, to obtain a sufficiently high amount thereof on the saturated sorbent, the method fails to produce a sufficiently high content of gold and silver on the saturated sorbent, a sufficiently full separation of gold, silver and impurities in the desorption zone, or a high recovery of gold and silver from the ores containing natural sorbents.